1. Field of the Invention
The present invention relates to an electronic blurring correction apparatus which electronically corrects blurring of an image formed on a solid-state image-capturing device.
2. Description of the Related Art
Among the image-capturing apparatuses for capturing a static image or dynamic image using a solid-state image-capturing device, there are quite a number of image-capturing apparatuses which can be held in hand to capture an image. In such image-capturing apparatuses, when, for example, the brightness of a subject is low, camera shake occurs easily because the shutter speed is slow. Further, in in-car cameras and the like as well, blurring can occur due to vibration of the vehicle during running.
Various technologies for correcting such blurring are proposed in the prior art, and several typical examples of those technologies are described hereinafter.
(1) Electronic blurring correction (Japanese Patent Application Laid-Open No. H6-46316 and the like)
In electronic blurring correction, an effective pixel region is made considerably smaller than the largest pixel region capable of capturing images by using an image-capturing device. When shooting using a digital camera equipped with an electronic blurring correction function, a shot image is temporarily recorded in a buffer memory first instead of being recorded immediately in a memory card. The digital camera shoots the next image immediately without pausing for a time interval. As with the first shot image, this second shot image is also recorded in the buffer memory first instead of being recorded immediately in the memory card. At this moment, if the position of the subject in the second shot image is misaligned (blurred) with the subject in the first shot image, the digital camera compares the first image with the second image, shifts the data region to be used so that the subject is fit in the screen in the same picture composition, and makes thus obtained region an effective pixel region in the second image. By using such a technology, image data can be recorded so that misalignment of the position of the subject is not caused between the images (i.e. blurring is not caused between the images).
(2) Optical blurring correction (Japanese Patent Application Laid-Open No. H10-336510 and the like)
The mainstream technology in optical blurring correction is a system in which when a vibrating gyroscope senses a movement of the camera, a part of the lens is moved in a direction of canceling blurring of a position where light reaches. By using such a technology, even when blurring might occur by a movement of the camera, the position of light reaching the image-capturing device first after the shutter is opened, and the position of light reaching the image-capturing device immediately before the shutter is closed can be made the same position to prevent blurring.
(3) Sensor shift blurring correction (Japanese Patent Application Laid-Open No. 2004-56581)
Sensor shift blurring correction is a technology for correcting blurring by moving an image-capturing device by the amount of blurring of the position where light reaches on an image capturing area, when a movement of the camera is sensed by a vibrating gyroscope. This technology has an advantage that blurring correction can be performed without basically causing deterioration of an image since part of the lens is not moved. This technology has a further advantage that blurring correction can be performed even when using a conventional interchangeable lens in which the blurring correction technology is not considered, since this technology can be applied in the camera main body of a camera with interchangeable lenses.
(4) Japanese Patent Application Laid-Open No. 2001-86398
In the image-capturing apparatus described in this patent application, a plurality of images, which are captured at exposure time intervals in which blurring does not occur, are read from an image-capturing device and stored in a buffer memory, and after image blurring (misalignment of the image positions) among the plurality of images stored in the buffer memory are corrected, the corrected images are added up to generate an image with no blurring. This technology is to perform electronic blurring correction and thus has an advantage that a complex mechanical mechanism is not required.
Incidentally, Japanese Patent Application Laid-Open No. H8-148667 describes a photoconductive film-stacked type solid-state image-capturing device. In the photoconductive film-stacked type CCD using such a technology, a photoconductive film for accumulating photoelectrically converted charges or converted charges is stacked on a CCD which performs horizontal scanning and vertical scanning, and a transparent electrode is further stacked on this photoconductive film.
However, the electronic blurring correction technology described above is a technology for preventing blurring of the composition or the position of a subject in a successive plurality of image data items, and is not a technology for correcting blurring which occurs only in the captured image. Specifically, even if blurring occurs in each image due to, for example, long exposure time, this technology cannot prevent such blurring, and thus cannot be effectively applied directly to blurring correction of a static image.
On the other hand, although optical blurring correction described above can be applied to blurring correction of a static image, the design is extremely complicated and the costs are high. Moreover, although blurring can be corrected, chromatic aberration, for example, increases to a certain degree, whereby the occurrence of deterioration on the optical performance is observed in viewing closely. Furthermore, unlike the electronic blurring correction technology, it is necessary to incorporate a mechanism for moving the lens, thus it is difficult to achieve reduction of the size of the digital camera or the like incorporated with such a mechanism. In addition, when applying this technology to, for example, a camera with interchangeable lenses, at least a part of the blurring correction mechanism needs to be incorporated in the lens side, thus the conventional interchangeable lens which does not respond to the blurring correction mechanism cannot perform blurring correction.
Sensor shift blurring correction described above is to drive the image-capturing device mechanistically, thus, as with the abovementioned optical blurring correction, it is difficult to achieve reduction of the size of the digital camera or the like incorporated with such a mechanism. Furthermore, if the image-capturing device is large, the amount of movement of the lens is also large, it is inevitable that the size of the mechanism increases. In addition, although it is important to move the image-capturing device only on an image-capturing plane surface which is perpendicular to the optical axis of a lens, it is difficult to prevent the occurrence of backlash, tilt of the image-capturing device with respect to the optical axis, and rotation of the image-capturing device around the optical axis.
Moreover, in the technology described in Japanese Patent Application Laid-Open No. 2001-86398 described above, readout of image data from the image-capturing device needs to be performed a plurality of times in order to obtain image data of one image. The more the number of pixels constituting the image-capturing device, the longer the time required for such readout from the image-capturing device. To cite a specific example, when reading out a pixel signal from an image-capturing device with 6 million pixels in a period of 30 [MHz], it requires 200 [ms] to only read out the signals of all pixels once. Therefore, when performing readout a plurality of times, time which is the integral multiple of 200 [ms] (or more) is required. On the other hand, for example, in a 35 mm film camera, if the focal length of a lens is f [mm], the maximum exposure time for roughly suppressing the occurrence of blurring is 1/f [seconds], which is empirically known. For example, when using a standard 50 [mm] shooting lens, the maximum exposure time is 20 [ms]. However, even 200 [ms] taken for reading out the image signals once from the image-capturing device is extremely long compared to the maxim exposure time of 20 [ms], thus reading out the signals a plurality of times takes considerably a long time. For this reason, it is considered that the technology described in this patent application is practical only in the limited conditions such as a small number of pixels of the image-capturing device and the long maximum exposure time for roughly suppressing the occurrence of blurring (for example, the short focal length of the shooting lens).
Therefore, it is desired to provide an electronic blurring correction apparatus capable of performing blurring correction in response to a broad range of shutter speeds, and a solid-state image-capturing device capable of adding up, at high speed, a plurality of images obtained at different times, without requiring a mechanical mechanism.